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What is sugar cane red rot and how do you deal with it?



The fungus that causes the disease is spread by wind, rain and insects. The disease can persist from year to year in soil, decaying leaves or crop stubble left over after raking. When a farmer plants already infected canes, the disease also spreads in the field.








India’s largest sugar cane producing state is Uttar Pradesh.





Sugarcane (Saccharum officinarum) family Gramineae (Poaceae) is a widely grown crop in India. As we know, India ranks second in the world in sugar cane production and the largest sugar cane producing state in India is Uttar Pradesh. It provides employment to over a million people directly or indirectly in addition to contributing significantly to the national treasury.












Red rot disease, also known as sugarcane crop cancer, can wipe out entire standing crops. Infection can reduce cane weight by 29% and lead to poor cane quality. Up to 25-75% sucrose is reduced in diseased cane compared to healthy cane.

Red rot is the most destructive disease of sugar cane. The disease affects every part of the plant above ground. The leaves gradually wilt downward as the disease progresses. The damaged leaf is often the third or fourth leaf from the top, and eventually the whole crown declines and wilts.

In severe cases, the cane shrinks and loses weight as the pith eventually dries out. The fungus begins to grow on the scab at this stage, often slightly below or above the nodes. When infected canes are split, they give off an alcoholic or sour starchy odor due to fermentation and show reddish areas. The attack of red rot begins from September to October.












The fungus that causes the disease is spread by wind, rain and insects. The disease can persist from year to year in soil, decaying leaves or crop stubble left over after raking. When a farmer plants already infected canes, the disease also spreads in the field.

Symptoms:

  • The affected canes leaf changes color from green to orange then to yellow in the third or fourth leaf and after that the leaves start to dry up from the bottom up.

  • If fungal microorganisms enter the leaf sheath through the midrib of the leaf, reddish spots may be seen on the back of the leaf midrib.

  • External symptoms do not appear until 16-21 days after infection and drying of the whole cane takes another 10 days.

  • When the affected cane is split, the inner region is reddish in color with intermittent white streaks along the length of the cane.

  • Sometimes the pith inside the cane is filled with a blackish-brown liquid and smells of alcohol.

Economic impact

A red rot disease was observed in the subtropical zone of Uttar Pradesh (UP) and Bihar, the main sugarcane region in India, during the growing season 1938–1939. This destruction led to the collapse of the important commercial variety Co 213, which destroyed thousands of hectares. Eastern UP sugar mills crushed only a third of their typical canes in 1938–1939 and a half in 1939–1940 due to a lack of cane supply.












Pathogen:

  • Red rot is caused by the fungus Glomerella tucumanensis. An older name, Colletotrichum falcatum, is still preferred by some pathologists.

Management

Cultural method:

  • The best way to control red rot is to select seedlings to plant from healthy plants in a disease-free area.

  • The field affected by red rot should be rotated with rice for one season and other crops for two seasons.

  • Cultivation of resistant and moderately resistant varieties recommended, namely Co 86032, Co 86249, CoSi 95071, CoG 93076, CoC 22, CoSi 6 and CoG 5.












Physical method:

  • Removal of affected bunches at an early stage and soaking the soil with Carbendazim 50 WP (1 g in 1 liter of water)

  • Cut ends and whole seeds should be soaked in a fungicide solution, such as 1% Bordeaux mixture.

  • If the disease is noticed in the field, the leaves and stems should be picked up and destroyed by burning.

Chemical method:

  • Adopt a plantation treatment with Carbendazim before planting (Carbendazim 50 WP (0.5 g in 1 liter of water) or Carbendazim 25 DS (1 g in 1 liter of water) with 2.5 kg of urea in 250 liters of water

  • Use fungi toxic chemicals like Bavistan, Benomyl, Topsin and Aretan at 0.1% for 18 min. at 52 ºC for seed soaking, which resulted in almost complete elimination of rot infection.











First Published: July 14, 2022, 05:58 IST



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